DRC Image Acquisition & Interpretation 2 — Questions and Answers
Question 1: A patient's mandibular molar periapical radiograph shows the apices cut off. Which receptor placement error caused this?
- Receptor placed too far anteriorly
- Receptor placed too close to the teeth
- Receptor not extended beyond the apices (Correct answer)
- Horizontal angulation error
Correct answer: Receptor not extended beyond the apices
The receptor must extend at least 5mm beyond the apex to ensure complete visualization of the root and periapical region.
Question 2: Which of the following best describes the appearance of a periapical abscess on a radiograph?
- Well-defined radiopaque area at the apex
- Poorly defined radiolucency at the apex (Correct answer)
- Widened lamina dura around the apex
- Hypercementosis at the root tip
Correct answer: Poorly defined radiolucency at the apex
A periapical abscess typically appears as a poorly defined (diffuse) radiolucency at or surrounding the root apex.
Question 3: When using the paralleling technique, the central ray should be directed:
- At a downward angle through the contact points
- Perpendicular to both the receptor and the long axis of the tooth (Correct answer)
- Parallel to the occlusal plane
- At a negative vertical angle for all mandibular teeth
Correct answer: Perpendicular to both the receptor and the long axis of the tooth
In the paralleling technique, the central ray is directed perpendicular to both the receptor and the long axis of the tooth to minimize distortion.
Question 4: Which of the following radiographic findings is characteristic of internal resorption?
- Radiopacity within the pulp canal
- Symmetric widening of the periodontal ligament space
- Round or oval radiolucency within the root canal (Correct answer)
- Resorption of alveolar crestal bone
Correct answer: Round or oval radiolucency within the root canal
Internal resorption appears as a round or oval-shaped radiolucency within the root canal, expanding the canal from within.
Question 5: A 'double image' artifact on a digital sensor is most likely caused by:
- Incorrect vertical angulation
- Movement of the receptor during exposure (Correct answer)
- Overexposure of the image
- Bending of the phosphor plate
Correct answer: Movement of the receptor during exposure
Movement of the receptor or patient during exposure causes a blurred or double image due to recording two positions simultaneously.
Question 6: Which landmark appears as a radiolucent 'Y' shape superimposed over the maxillary premolar region?
- Incisive foramen
- Maxillary sinus and nasal fossa junction (Correct answer)
- Median palatine suture
- Nasolacrimal canal
Correct answer: Maxillary sinus and nasal fossa junction
The inverted 'Y' (or 'Y of Ennis') is the intersection of the anterior wall of the maxillary sinus and the lateral wall of the nasal fossa, typically seen in the premolar region.
Question 7: On a bitewing radiograph, the image of the crowns of maxillary and mandibular teeth appears equally sharp but the roots are cut off. What is the most likely cause?
- Excessive positive vertical angulation (Correct answer)
- Receptor placed too high in the palate
- Cone-cut error
- Incorrect horizontal angulation
Correct answer: Excessive positive vertical angulation
Excessive positive vertical angulation on bitewing radiographs causes the receptor to not capture the apical areas and can result in foreshortening or distortion.
DRC Image Acquisition & Interpretation 2
A patient's mandibular molar periapical radiograph shows the apices cut off.
Which receptor placement error caused this?